1. Field of the Invention
The present invention relates to a method for the radio coverage of a mobile terminal of a mobile radio network in the catchment area of an intermediate station which is used as a adverter.
2. Description of the Prior Art
The subscribers of such a modern mobile radio network can be currently reached at almost any location in the world. However, the general problem is that the connection to the mobile radio network is broken for subscribers entering a relatively large building, due to shielding by metal constructions or window frontages with metallized windows. This problem has hitherto been solved by installing base stations of the mobile radio network operator inside correspondingly large and mostly public buildings so that this area, too, is covered by the mobile radio network itself.
This procedure has the disadvantage that the officially issued frequencies of the mobile radio network must be used and the base stations must also must be connected to the normal landline network of the mobile radio network operator.
On the other hand, there is also the possibility of using subsystems which communicate on frequencies not belonging to the public mobile radio network with mobile terminals in the in-house area. In these systems, however, the communication is such that an early decision is made, by choosing either a corresponding mobile terminal for the corresponding frequency or, in the case of mobile terminals having combined frequency systems, by selecting a certain frequency or a certain mode, whether connection is established with the public mobile radio network or with an in-house cordless telecommunication network. In any case, this does not solve the problem of the transition from a public mobile radio network to an in-house mobile radio network.
From DE 195 32 635, a digital telephone system for wireless communication with a fixed station, a mobile handset and a regenerator/converter device is known in which the mobile handset can be assigned both first frequencies of a first frequency band and second frequencies of a second frequency band which is disjoint from the first frequency band and the regenerator/converter device is provided with a first and a second radio interface, in which arrangement first frequencies can be assigned to the first radio interface and second frequencies can be assigned to the second radio interface and in which the first radio interface has the functionality of a mobile handset and the second radio interface has the functionality of a fixed station.
It is an object of the present invention, therefore, to specify a method which describes the problem of transition from a public mobile radio network to an in-house mobile radio network, a case distinction having to be made with respect to the entry and the exit into the in-house area of reception, and the new setting-up of a connection in the in-house area to the mobile radio network.
Accordingly, the present invention is directed to a method for the radio coverage of a mobile terminal of a mobile radio network wherein, in the case of an existing connection between the mobile radio network and a mobile terminal which approaches the internal area of reception of an intermediate station, a connection is first set up between this mobile terminal and this intermediate station on the internal frequency, via which connection the individual features of the mobile terminal are handed over to the intermediate station and then a handover of the connection takes place between mobile terminal and mobile radio network due to which a connection from the mobile radio network via the intermediate station to the mobile station is produced. These method steps thus take into consideration the situation of a mobile terminal which is already communicating with the mobile radio network on entry into the internal area of reception of an intermediate station.
In another embodiment, the method of the present invention also takes into consideration the situation when a mobile terminal has set up a connection to the mobile radio network via an intermediate station and is now leaving the internal area of reception of the intermediate station. Accordingly, in the case of an existing connection from a mobile terminal via an intermediate station to the mobile radio network, the intermediate station detects a removal of the mobile terminal from the internal area of reception of the intermediate station, forwards the frequency and the connection information to the mobile radio network to the mobile terminal and then a handover of the mobile radio network-intermediate station-mobile terminal connection to the mobile radio network-mobile terminal connection takes place.
According to another embodiment of the present invention, the method is improved to the extent that, in the case when a new connection is set up from the mobile terminal to the mobile radio network, for setting up the connection, the mobile terminal first, or after an unsuccessful connection set-up attempt with a mobile radio frequency, attempts to establish a connection to an intermediate station on an internal frequency.
According to another embodiment of the present invention, it is also possible that a combination of the characterizing features of each of the above there embodiment can occur depending on the situation of the movement of the mobile terminal.
According to a further embodiment of the present invention, the connections can operate, for example, in accordance with the TDMA (Time Division Multiple Access) method and/or the FDMA (Frequency Division Multiple Access) method and/or the CDMA (Code Division Multiple Access) method.
According to yet another embodiment of the method described above, it is proposed that the intermediate station converts an incoming signal according to the FDD (Frequency Division Duplex) method to an outgoing signal according to the TDD (Time Division Duplex) method and, on the other hand, converts an incoming signal according to the TDD method to an outgoing signal according to the FDD method. As a rule, the incoming signal according to the FDD method will be a signal of the mobile radio network whereas the signal according to the TDD method will be associated with the in-house radio network.
A further advantageous embodiment of the method according of the present invention consists in that, before a connection is taken over by the intermediate station, an exchange of a PIN (Personal Identification Number) takes place between the mobile terminal and the intermediate station and that the handover procedure is only initiated if the mobile terminal is authorized on the basis of the PIN. The prerequisite for this is, naturally, that the intermediate station has a data memory in which the PINs of the authorized subscribers are stored.
To detect an approaching mobile terminal, it can be advantageous if the intermediate station periodically monitors the at least one internal frequency for a message sent by an approaching mobile terminal. Naturally, the mobile terminal must also periodically send out corresponding messages to carry out this method.
In the reverse case, it also can be advantageous if, to detect the penetration of a mobile terminal into the internal area of reception of the intermediate station, the mobile terminal itself monitors the internal frequency periodically for messages sent by an intermediate station. For this purpose, it is necessary, in turn, that the corresponding intermediate station sends out such messages periodically via its internal frequency.
Another advantageous embodiment of the method of the present invention contemplates, that the intermediate station, to detect the migration of the mobile terminal out of the internal area of reception, evaluates the bit error rate occurring during the communication between intermediate station and mobile terminal and, when a predetermined value is exceeded, assumes that the mobile terminal is migrating away.
Another advantageous embodiment of the method with respect to the detection of the emigration of the mobile terminal from the internal area of reception of an intermediate station, contemplates that the intermediate station measures the transmit and receive power of the mobile terminal at regular intervals or continuously and, when the power drops below a certain level, assumes that the mobile terminal is migrating out of the internal area of reception.
Other advantageous embodiments of the method consider, for example, that the intermediate station also communicates with a landline network in addition to its connection with the mobile radio network. This can be, for example, an ISDN (Integrated Services Digital Network) or a PSTN (Public Switched Telephone Network).
It is also advantageous in a communication between the intermediate station and a landline network and a radio network if the intermediate station can either independently switch between both networks or switches on request by the mobile terminal.
The mobile radio network currently to be considered is, for example, a GSM (Global System for Mobile Communications) network or a UMTS (Universal Mobile Telecommunication System) network. To actually implement the method of the present invention, for example in a GSM network, it is necessary to provide some still available GSM frequencies for the in-house area. In the case of a UMTS network, it can be assumed that some frequencies will be provided for the in-house area from the start. The advantage resulting from the provision of such in-house frequencies lies in the fact that the frequency planning for the external area is in no way influenced. A further advantage of the method represented lies in the fact that the intermediate station is only connected to the GSM/UMTS base stations via an air interface and only simulates a mobile terminal with respect to this base station. In this manner, the remaining network infrastructure remains completely free of reactions as a result of which a corresponding method also can be integrated without extra cost to the operators of the mobile radio networks.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Preferred Embodiments and the Drawings.